But in a complex case, the other pair were convicted over a payment of HK$8.5 million made to Hui in the four days leading up to his 2005 appointment to the government's second-highest post.

Hui, the most senior official ever arrested for graft, was found guilty on five of eight charges against him. Thomas Kwok was convicted of one count of conspiracy to commit misconduct in public office and cleared on another two charges.

Hui, who prosecutors said enjoyed an extravagant standard of living that far outstripped his official salary, was also found guilty on charges relating to rent-free use of luxury apartments and acceptance of unsecured loans.

The Kwok brothers, aged 63 and 61, jointly chair development giant Sun Hung Kai Properties and were arrested along with Hui in a major swoop by graft investigators two years ago.

Prosecutors said fat bribes were made to Hui, who served as chief secretary from June 2005 to June 2007, through a series of complicated transactions involving middlemen.

Two of the middlemen, Sun Hung Kai director Thomas Chan and Francis Kwan -- the former non-executive director of investment firm New Environmental Energy Holdings -- were both found guilty on two counts in the trial.

'Black eye' for Hong Kong

The case has stunned Hong Kong, where Sun Hung Kai is the biggest property developer by market capitalisation and owns some of the city's most recognisable real estate including the 118-floor International Commerce Centre.

The two brothers are ranked 62 on the Forbes rich list and are worth an estimated $14.45 billion dollars.

"It's a big black eye for the integrity of Hong Kong," said Francis Lun, a financial analyst and CEO of Hong Kong-based Geo Securities.

"The last thing you would expect is corruption at the top," he told AFP, adding that the city has had a well established anti-graft body since the 1970s.

"I suspect this isn't an isolated case, there must be other big business eyeing into the government too," he said.